Circulating tumor cells (CTCs) are primary tumor cells that have shed into the vascular system and are potentially present across the body, particularly in the bloodstream. CTCs may serve as seeds for metastasis in locations divergent from the primary tumor, posing a substantial health risk to the cancer patient. Research indicates that CTCs derive from clones in the primary tumor and that they serve an important role in the metastatic spread of carcinomas. It has been demonstrated that CTCs reflect molecular features of cells within the primary tumor, thus enabling characterization of the tumor without a biopsy of the primary tumor. CTCs also represent metastasis in action, and therefore, monitoring and analyzing CTCs is indicative of the patient's disease status. CTCs are not easily analyzed because they are present in very small numbers in blood. For example, CTCs may be found in frequencies of about 1-10 CTC per mL of whole blood in patients with a metastatic disease. This small number contrasts with the other cellular components within one mL of blood, (e.g. a few million white blood cells, a billion red blood cells). Thus, using CTCs for diagnostic purposes relies on the ability to isolate or identify the CTCs within a vast matrix of other cells. Furthermore, the rarity of the cells in a sample enhances the value of the sample as analytical targets. CTCs are presently known to be present in several epithelial cancers (e.g., breast, prostate, lung, and colon) and clinical evidences indicate that patients with metastatic lesions are more likely to have isolatable CTCs.